Port Adelaide midfielder Matt Thomas is the first player to be suspended under the AFL's crackdown this season on umpire contact.

The tribunal jury found him guilty of recklessly making contact with field umpire Jason Armstrong during Saturday's upset win over Hawthorn.

Port Adelaide unsuccessfully tried to have the charge from reckless to negligent because Thomas' 20 per cent loading for a previous offence meant he could not escape with a reprimand.

The suspension means he will miss Friday night's big clash at AAMI Stadium against unbeaten St Kilda.

He was also fined $2600.

Also on Tuesday night, 2002 Brownlow Medallist Simon Black pleaded guilty to reckless umpire contact and escaped with a reprimand and a $1950 fine.

He was able to receive a 25 per cent discount on the match review panel's recommended penalty of 125 demerit points and a $2600 fine - the same punishment suggested for Thomas.

Black remains eligible for the Brownlow, even though he pleaded guilty, because the matter was referred directly to the tribunal.

Usually, a player becomes ineligible for the Brownlow if the original penalty was above the 100-point threshold for a one-game suspension.

But in his case the penalty was only a recommendation, not a set punishment under the tribunal system's points system.

A fortnight ago, Sydney co-captain Brett Kirk also received a reprimand after he pleaded guilty to reckless umpire contact.

All three cases have involved players setting up behind the umpire at a ruck contest.

In Tuesday's other case, St Kilda onballer Leigh Montagna was found not guilty of striking.

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